This invention relates to a multi-step automatic transmission for motor vehicles having a plurality of clutches and brakes designed at least partly as wet-running, multi-disk clutches with inner and outer disk carriers each provided with one set of disks.
Multi-step automatic transmissions for motor vehicles are widely known. EP-B 434 525 thus describes an automatic transmission for motor vehicles which has planetary gear sets shifted by means of clutches and brakes and connected with a hydraulic torque converter provided with a lock-up clutch. The automatic transmission further has an input shaft and an output shaft with a double planetary gear set, at least one power path between the input shaft and the double planetary gear set, the same as three clutches and two brakes, the selective engagement by pairs of which determines different reduction ratios between the input shaft and the output shaft. Six forward gears and one reverse gear can be obtained by the three clutches and two brakes.
In motor vehicles having automatic transmissions, there occur in certain situations such as during positive and negative load change, shifting jerks that impair the comfort. In order to prevent such a shifting jerk during the gear shift of the automatic transmission, it was already proposed in DE-C 29 35 916 that the torque of the internal combustion engine be reduced during the gear shift. Together with the reduction of the shifting jerk, it is also possible, by virtue of the torque of the internal combustion engine reduced during the shifting process, to reduce the grinding time of the friction clutches of the automatic transmission that take part in the gear shift so that less wear and slighter heating of the friction elements occur. The control electronic system for the internal combustion engine is equipped with an identification shifting system which, during gear shift, receives from the transmission control a shifting signal. In a memory of the control device for the internal combustion engine characteristic fields are stored according to which the ignition angle and/or the injection pulse width are controlled according to load and rotational speed. The exact detection of the moment of reduction of the torque is problematic here.
DE-A 40 37 092 describes a method for control of the torque by means of an internal combustion engine connected with an automatic transmission which is driven by the internal combustion engine, there being associated with the latter a control electronic system, which based on rotational speed, load and optionally temperature signals, controls the ignition angle of the ignition device and/or the injection pulse width of the fuel injection device. A transmission electronic system associated with the automatic transmission controls for its part, based on rotational speed and load requirement signals, the gear shifts of the automatic transmission.
One other possibility of improving the comfort in shifting consists in associating with the engine electronic system so-called comfort filters as dampers of load change and jerks, the periods of time of the comfort filters between the driver""s wish and ratio of the inner engine being preset exclusively by the electronic system of the internal combustion engine.
Another problem in modern multi-step automatic transmissions consists in that, on one hand, to maintain very high static torques with one clutch and, on the other, with the same clutch to govern gear shifts with slight load or rolling out gear shifts absolutely without load, creates serious problems. In the design of the clutch, compromises have to be made here which impair the comfort during shifting.
The problem to be solved by this invention is to configure a multi-step automatic transmission for motor vehicles so that the impairments to comfort in shifting do not occur.
Based on a multi-step automatic transmission of the kind specified above, the problem is solved with the features stated in the characteristic part of claim 1; advantageous developments are described in the sub-claims.
The invention, therefore, proposes that the piston space of the clutch is divided by a baffle plate for the hydraulic oil so that first and second pressure chambers are formed configured so that the total stroke of the piston is not impaired.
The baffle plate can be located inside or outside the clutch; inasmuch as the required differential surface is not obtained by the two pressure chambers separated from each other by the baffle plate, each pressure chamber is advantageously provided with a fluid pipe so that the two pressure chambers can be loaded with different pressures.
Therefore with the inventive development, the advantage obtained is that by providing a differential surface on the same clutch, the large piston surface needed for the high static retaining torque of the clutch is reduced so that the gear shifts can be reduced according to the differential surface; this means an optimal adaptation of the clutch to high retaining torques and low shifting torques without an additional clutch that increases the expenses. The differential surface formed here is easily controlled by the electronic control unit of the transmission.